The present invention relates to a clamp centering device provided in an optical disc player for centering an optical disc, and more particularly to a clamp centering device for a double-sided optical disc.
There is a certain type of optical disc (for example, a video disc) which comprises two discs adhered to each other at the back thereof so that the thus assembled disc has double recording surface, namely side A and side B. In order to reproduce both the sides A and B, an optical pickup is provided to be moved to the respective sides. Thus, once the assembled disc is set on a turntable of a disc player, the double side can be continuously played by the pickup so that the user need not bother to flip over the disc.
However, when adhering the two discs, center holes thereof may not always accurately coincide with each other. In order to correct the deviation of the assembled disc on the turntable, Japanese Utility Model Application No. 63-8852 discloses a centering device. The centering device has a pair of centering mechanisms, each for one of the sides A and B, and one of the mechanisms is selectively operated depending on the side to be played. Furthermore, Japanese Patent Application No. 6-129727 discloses a centering device having a complicated structure.
The video disc is usually employed with the adhered double-sided disc. In a video disc player in which an optical pickup is provided only on an underside portion of the disc, the clamp centering device is provided to center a center hole of a lower side disc only. In a double-sided disc player in which an optical pickup is moved to both sides of the disc, the centering device has two centering mechanisms for both sides.
On the other hand, the recording density of the recording medium has been increased. In an adhered multi-layered disc such as a DVD having a compact size and a high density of the signal pit, it is necessary to heighten the accuracy of the centering mechanism. Additionally, it is an important factor to reduce manufacturing cost of the player. In particular, since the diameter of the multi-layered disc is smaller than the laser disc, the diameter of the center hole is small. Thus, the quality of the centering mechanism may affect the player.
FIG. 5 shows a conventional centering device for centering a double-sided disc 501 comprising a lower side disc and an upper side disc. The centering device has a hollow turntable 102 on which the disc 501 is set. The turntable 102 is fixedly mounted on a rotating shaft 104. The rotating shaft 104 is connected to a spindle motor 108. A centering hub 503 is axially slidably mounted on the rotating shaft 104 inside the turntable 102. A spring 109 is provided between the bottom surface of the turntable 102 and the lower end of the centering hub 503, thereby engaging the centering hub 503 with the center hole of the disc 501. The centering device further has a clamper 105 which cooperates with the turntable 102 to clasp the disc 501 therebetween. On an upper portion of the clamper 105, a magnet 106 and a back yoke 107 are provided. By the clamper 105, magnet 106, back yoke 107 and turntable 102, a magnetic circuit is formed so as to attract the disc 501 to the turntable 102. The turntable 102 is rotated by the spindle motor 108 through the rotating shaft 104.
When playing the disc 501, the center hole of the disc 501 is carried to a position above the center of the centering hub 503 by a disc tray (not shown), and then the disc is lowered on the centering hub. At that time, the disc is lowered, sliding the inside wall of the center hole of the disc on an upper slant of the centering hub. Thereafter, the disc is pushed toward the turntable 102 by the clamper 105. The disc 501 and the centering hub 503 are lowered together to the turntable 102, while the lower periphery of the inside wall of the center hole is engaged with the slant of the centering hub 503. Thus, the disc 501 is clamped on the turntable 102 by the clamper 105 to be interposed between the clamper and the turntable. In this state, the disc 501 is so positioned that the lower side disc is centered by the slant of the centering hub 503. As a result, the upper side disc of the disc 501 is not centered.
In such a structure, when recording or reproducing the upper and lower side discs without flipping over the disc 501, if the upper side disc is largely deviated from the center, inconvenience may occur.
In order to prevent the inconvenience, the above described double centering mechanism has been proposed for both sides.